#include <iostream>
#include<map>
using namespace std;
int main()
{
  char ch;
  map<char,int>m;
  while(cin>>ch)
    if(m.find(ch)==m.end())m[ch]=1;
    else m[ch]++;
  for(auto val:m)
    if(val.second!=1){
      cout<<"NO"<<endl;
      exit(0);
    }
    cout<<"YES"<<endl;
  return 0;
}